EP0743106B1 - Verfahren zur Herstellung eines nahtlosen Rohres - Google Patents

Verfahren zur Herstellung eines nahtlosen Rohres Download PDF

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Publication number
EP0743106B1
EP0743106B1 EP96107907A EP96107907A EP0743106B1 EP 0743106 B1 EP0743106 B1 EP 0743106B1 EP 96107907 A EP96107907 A EP 96107907A EP 96107907 A EP96107907 A EP 96107907A EP 0743106 B1 EP0743106 B1 EP 0743106B1
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EP
European Patent Office
Prior art keywords
plug
piercing
billet
steel
alloy
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP96107907A
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English (en)
French (fr)
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EP0743106A1 (de
Inventor
Tatsuro Katsumura
Takashi Ariizumi
Motoharu Yamazaki
Masahiko Yasukawa
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JFE Engineering Corp
Original Assignee
NKK Corp
Nippon Kokan Ltd
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Filing date
Publication date
Priority claimed from JP14567395A external-priority patent/JPH08309408A/ja
Priority claimed from JP16282495A external-priority patent/JPH08332504A/ja
Priority claimed from JP07168634A external-priority patent/JP3085149B2/ja
Application filed by NKK Corp, Nippon Kokan Ltd filed Critical NKK Corp
Publication of EP0743106A1 publication Critical patent/EP0743106A1/de
Application granted granted Critical
Publication of EP0743106B1 publication Critical patent/EP0743106B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
    • B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
    • B21B19/04—Rolling basic material of solid, i.e. non-hollow, structure; Piercing, e.g. rotary piercing mills
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B25/00—Mandrels for metal tube rolling mills, e.g. mandrels of the types used in the methods covered by group B21B17/00; Accessories or auxiliary means therefor ; Construction of, or alloys for, mandrels or plugs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B25/00—Mandrels for metal tube rolling mills, e.g. mandrels of the types used in the methods covered by group B21B17/00; Accessories or auxiliary means therefor ; Construction of, or alloys for, mandrels or plugs
    • B21B25/04—Cooling or lubricating mandrels during operation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B17/00—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling
    • B21B17/08—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling with mandrel having one or more protrusions, i.e. only the mandrel plugs contact the rolled tube; Press-piercing mills
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/4981—Utilizing transitory attached element or associated separate material

Definitions

  • the present invention relates to a method for manufacturing a seamless pipe, and more particularly, to a method for manufacturing a seamless steel pipe and a seamless metal pipe.
  • a seamless steel pipe is produced by preparing a billet having a round or a square cross-section, forming a hollow shell by a method such as Mannesmann piercing, press piercing or hot extrusion, and rolling the thus-formed hollow shell by a rolling mill such as an elongater, plug mill or a mandrel mill and subjecting the rolled hollow shell to a sizing work performed with a sizer or a stretch reducer, whereby the final pipe product of a predetermined size is obtained (hereinafter called a "continuous rolling process").
  • the piercing plug for use in Mannesmann piercing and press piercing is always held in contact with a billet heated to a high temperature of 1100 to 1300 °C, and the plug is required to sustain heavy load. Therefore, the piercing plug is damaged during the piercing work.
  • a conventional piercing plug is able to withstand several hundreds of piercing cycles when used for piercing a billet made of, for example, a carbon steel (a low-alloy steel), the piercing plug is damaged considerably as shown in Figs.
  • Figs. 4 and 5 when used to pierce billets made of a high-alloy steel exemplified by a stainless steel such as 13 Cr steel, SUS 304 and SUS 316, or a high alloy (hereinafter called a "high-alloy steel or the like"), the main component of which is Cr, Ni or Mo, represented by a high alloy containing, as main component thereof, not lower than 25 wt% Ni.
  • Figs. 4 and 5 are side views showing a damaged piercing plug. Referring to Figs.
  • reference numeral 1 represents a piercing plug itself
  • 5 represents a deformation of the leading end due to melting
  • 6 represents a crease damage in the body
  • 7 represents a seizure of the material of the piercing plug.
  • the prior art 2 encounters with difficulty in the supply of lubricant in successive piercing cycles, although it can eliminate seizure between the billet and the plug in at least the first piercing cycle.
  • Supply of lubricant is possible by a different method: namely, through the head of the plug via a passage formed in a plug bar in support of the plug. This method, however, involves a problem in regard to damaging of the plug end or clogging of the same and, hence, cannot be continuously used in actual piercing mills.
  • a technique considered to be most widely used and in which a piercing plug made of a low-alloy steel, such as 3Cr-1Ni (hereinafter called a "known component") is subjected to heat treatment prior to performing the piercing work to use the produced surface scale as the lubricant is advantageous in view of improving durability similarly to the conventional piercing method.
  • the obtained piercing plug can be used in only about 10 cycles which is unsatisfactory as compared with the case where the same is used to pierce common steels. Thus, reduction in the tool cost and improvement in the efficiency in the rolling work cannot be realized.
  • the prior art 1 relying upon the use of Mo as the plug material has many advantages such as prevention of deformation of the plug itself, prevention of seizure, and so forth.
  • Mo is expensive and the plug made of this material is rather fragile in a temperature range of about 400°C or less. Due to the foregoing fact and a fact that the plug of the foregoing type can easily be broken due to thermal stress, there are many problems in using industrially.
  • the prior art 3 is able to prevent damage of the plug because a abrasion resistance layer is provided, the abrasion resistance layer made of hard material can easily be cracked due to repeated thermal stress and the layer subjected to the heat treatment separates easily. This method therefore has not yet been matured to such a level as to be practically used on actual machines.
  • plugs have been disclosed in Japanese Patent Laid-Open No. 2-207503 (hereinafter called a "prior art 5”) and Japanese Patent Laid-Open No. 62-244505 (hereinafter called a “prior art 6”) as a means capable of elongating the life of the piercing plug and enabling the piercing plug to be manufactured at low cost in which Mo or a Mo alloy or ceramics exhibiting excellent wear resistance is disposed at the leading end of the plug and the body is subjected to the conventional oxidation process or structure.
  • the plug disclosed in the known arts 5 and 6 (hereinafter called a "composite plug") has the structure such that only the leading portion of the plug, which is applied with a large stress and load, is made of the foregoing strong material, such as Mo, because the cost is enlarged excessively is the overall body of the piercing plug is made of the foregoing material, and the other portion is made of a low-cost alloy steel to reduce the cost of the tool.
  • the cost per one piercing operation can be reduced to the cost required for the conventional technique and an effect can be improved because the efficiency in the rolling operation can be improved.
  • the foregoing technique cannot reduce the thermal stress taking place due to the friction between the material of the billet and the body of the plug during the operation. Therefore, cracks taking place due to the thermal stress cannot be prevented.
  • the oxidation scale applied to the body of the plug is similar to that applied in the conventional techniques, damage of the body due to the piercing work results in the quality and accuracy of a product being excessively deteriorated in its internal surface even if the head of the plug is sound for use. As a result, the manufacturing cost cannot be reduced.
  • a disc is laid on the ingot, through which disc the mandrel has to pierce before entering the ingot, the disc being heated before piercing.
  • material for the disc iron or unalloyed steel is used. It is preferable that the disc material be one which can be welded to the ingot. This can be done before heating the disc, so that the ingot and disc are jointly heated.
  • the material of the disc gradually flows down over the rim of the front end of the mandrel and is deposited as a firmly adhering coating on the wall of the pierced hole. In this way, the material of the metal disc is distributed between the peripheral surface of the mandrel and the internal surface of the hollow ingot.
  • the piercing plug is made of the alloy steel of the conventional component or the low-alloy steel, heat applied to the plug from the material to be pierced or rise in the temperature due to heat generated during the work of the material results in the strength being allowed to deteriorate. Thus, the piercing plug is melted and deformed due to the load applied during the piercing work.
  • the piercing plug made of the alloy steel is used to pierce a work piece (billet) which damages the piercing plug
  • use of the wear-resisting plug having a hardened surface or a plug made of a heat-resisting alloy or Mo or a Mo alloy result mainly in the surface being cracked.
  • the durability of the plug cannot be improved.
  • damage of the body of the plug inhibits solving of the problem. Therefore, a method of elongating the life of the piercing plug having effects in reducing the manufacturing cost and improvement in the efficiency in the rolling work has not been established yet.
  • the present invention provides a method for manufacturing a seamless pipe as described in claim 1.
  • the billet can be made of an alloy steel containing Cr in an amount of at least 5 wt%, or an alloy steel containing Ni in an amount of at least 5 wt%.
  • the billet can be made of an alloy, the main component of which is selected from the group consisting of Cr, Ni and Mo.
  • the piercing plug comprises a main body made of any one of Mo, a Mo alloy and a heat-resisting steel and a hard layer formed on the surface of the main body.
  • the hard layer is made of any one selected from a group consisting of stellite, ceramics obtained by adding tungsten carbide to stellite, ceramics obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and ceramics obtained by adding a compound of chromium and carbon to stellite.
  • the piercing plug comprises a plug body made of any one of Mo, a Mo alloy and a heat-resisting steel and a plug head formed at the leading end of the plug body and made of any one of Mo, a Mo alloy and a heat-resisting steel.
  • the plug body can have a hard layer formed on the surface of the plug body.
  • the plug head can have a hard layer formed on the surface of the plug head.
  • the method according to the present invention may comprise the step of the steel plate being subjected to an oxidation treatment.
  • the steel plate can be made of a carbon steel. Also, the steel plate can be made of an alloy steel containing one element selected from the group consisting of C in an amount of less than 5 wt%, Cr in an amount of less than 5 wt% and Ni in an amount of less than 5 wt%. Moreover, the steel plate can be made of an alloy steel containig Si in an amount of 1 wt% or more. The steel plate can be joined to the billet by welding.
  • the piercing plug satisfies the following equation : 0.8 ° ⁇ ⁇ - ⁇ ⁇ 1.5 ° wherein ⁇ is an angle of a plug reeling portion and ⁇ is an angle at an outlet portion of a roll.
  • the method for manufacturing a seamless pipe of the embodiment-1 comprises the steps of : preparing a billet ; joining a steel plate to at least an end surface ; preparing a piercing plug ; hot-piercing the billet to produce a hollow shell ; and rolling the hollow shell to produce a seamless pipe.
  • the billet is made of an alloy steel or an alloy.
  • the alloy steel is selected from an alloy steel containing Cr in an amount of at least 5 wt%, or an alloy steel containing Ni in an amount of at least 5 wt%.
  • the alloy includes one element selected from the group consisting of Cr, Ni and Mo as the main component.
  • the steel plate is joined at least to an end surface at which piercing of the billet is commenced.
  • the steel plate can be joined at both end surface of the billet.
  • the piercing plug is made of Mo, a Mo alloy or a heat-resisting steel.
  • the billet, to which the steel plate is joined, is hot-pierced to produce a hollow shell.
  • the hollow shell is rolled to produce a seamless pipe.
  • the piercing plug comprises a main body made of any one of Mo, a Mo alloy and heat-resisting steel and a hard layer formed on the surface of the main body.
  • the hard layer is made of any one selected from the group consisting of stellite, ceramics obtained by adding tungsten carbide to stellite, ceramics obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and ceramics obtained by adding a compound of chromium and carbon to stellite.
  • the piercing plug comprises a plug body made of any one of Mo, a Mo alloy and a heat-resisting steel and a plug head formed at the leading end of the plug body and made of any one of Mo, a Mo alloy and a heat-resisting steel.
  • the plug body can have a hard layer formed on the surface of the plug body.
  • the plug head can have a hard layer formed on the surface of the plug head.
  • the inventors of the present invention measured the surface temperature of the piercing plug made of Mo or the Mo alloy under conditions of piercing by using a model piercing mill similar to conditions when an actual mill is used. To make a comparison, also a plug which is used to pierce an alloy steel, which is made of a low-alloy steel and which has been subjected to an oxidation treatment was tested similarly. Results were shown in Fig. 6. Referring to Fig.
  • mark ⁇ represents a piercing plug made of Mo or the Mo alloy (a plug having a metal surface subjected to no treatment)
  • square and solid black mark ⁇ represents a plug (a plug with oxidation scale) made of a low-alloy steel and subjected to the oxidation treatment.
  • the temperature of the surface of the plug having the surface subjected to no treatment is always higher than that of the plug with oxidation scale having scales on the surface thereof.
  • the foregoing fact can be applied regardless of the material of the plug, even if the material of the plug is the heat-resisting steel or the Mo alloy.
  • the plugs were cooled to the room temperature by air-cooling or mist cooling, followed by performing several times the piercing operation.
  • the heat-resisting steel is, in the embodiment-1, defined to be a steel "having a tensile strength of 30 N/mm 2 in the "high-temperature tension test at 1100°C conforming to JIS G0567".
  • the plug previously heated prior to performing the piercing work and used in the piercing work in such a manner that the lowest temperature of the surface was set to be about 400 °C, and a plug having a hardened surface such that the hard layer was formed on the surface by metal-spraying were forcibly cooled from the inside of the plugs.
  • generation of defect could not be confirmed even after 10 times of the piercing work.
  • the plug having the surface on which the hard layer had been formed and the plug having poor resistance against thermal stress including the composite plug must be contrived such that rise in the surface temperature is inhibited.
  • the inventors of the present invention discovered use of oxidation scale capable of effectively serving as a heat insulating layer. That is, the discovered method is not the conventional method in which the piercing plug is previously subjected to an oxidizing treatment or a method shown in Fig. 8 and using a plug protective cover subjected to the previous oxidizing treatment.
  • the conventional methods involves loosing oxidation scale serving as the heat insulating layer whenever the piercing work is performed.
  • the discovered method is a method in which as shown in Fig. 7 scale is supplied from the billet and the oxidation scale is supplied to the plug whenever the piercing work is performed.
  • the supply of the oxidation scale from the billet portion according to the present invention is capable of performing a similar operation which can be performed by a treatment for forming a oxidation scale film due to heat treatment.
  • a treatment for forming a oxidation scale film due to heat treatment By using the foregoing supply, rise in the temperature of the surface of the piercing plug can be prevented as shown in Fig. 9.
  • white and square mark ⁇ represents a plug (plug according to the embodiment-1) to which oxidation scale has been supplied from the billet portion
  • black and square mark ⁇ represents a plug subjected to the process of forming the oxidation scale (the plug with the oxidation scale).
  • the oxidation scale which has been enabled to be formed on only the conventional plug made of the alloy steel, can be formed on a plug made of Mo or the Mo alloy, which is sublimated at high temperatures.
  • the life can effectively be elongated.
  • the oxidation scale can be formed on the billet made of a high-alloy steel or the like, the foregoing effect cannot be expected from only the end surface of the billet in a case where the quantity of oxidation scale, which can be formed, is considerably small as compared with that in the case of the carbon steel or the low-alloy steel.
  • the thermal stress generating in the plug can be prevented, generation of cracks can be prevented and the durability of the plug can be elongated.
  • the plug having the surface on which a hard layer (hereinafter called a "hard layer”) exhibiting satisfactory strength and/or wear resistance even under high atmospheric temperatures is formed for example, a layer made of 30Cr-Co base alloy (stellite) or ceramics having a composition in which WC, WC-Co or Cr 2 C system is added to stellite, a reason similar to that described above can be employed. That is, the issue that foregoing method having advantage as compared with the conventional plug cannot be employed because of separation of the hard layer taking place due to thermal stress can effectively be overcome by the method according to the embodiment-1 because the method is able to prevent separation.
  • a hard layer for example, a layer made of 30Cr-Co base alloy (stellite) or ceramics having a composition in which WC, WC-Co or Cr 2 C system is added to stellite
  • the oxidation scale effectively serving as a heat insulating material is able to prevent thermal stress generating between the surface thereof and the base material of the plug.
  • usual ceramics can be employed to form the hard layer as shown in Table 4.
  • the foregoing fact is also applied, for example, to the composite piercing plug formed to comprise a plug body and a plug head formed at the leading end of the plug body.
  • deformation of the plug body which has been considered a sole problem, can very effectively be prevented.
  • a case where the foregoing hard layer is formed in the plug body and/or the plug head of the composite plug is similarly applied.
  • any method may be employed, for example, metal-spraying, plating, a TD (VC) process, PVD (physical vaporization deposition) and CVD (chemical vaporization deposition).
  • VC TD
  • PVD physical vaporization deposition
  • CVD chemical vaporization deposition
  • a billet formed by joining a steel plate 9 made of a general carbon steel to the end surface (hereinafter called a "leading end surface") of a billet 8 made of 13Cr on which piercing is commenced, and a billet having no steel plate joined thereto and made of general 13Cr were used.
  • the material of a piercing plug 1 having a shape shown in Fig. 1 was varied within and without the scope of the embodiment 1.
  • Mannesmann piercing method was employed with an apparatus having a pair of rolls consisting of at least two rolls and two shoes to perform piercing under the following piercing conditions. The life of each of the used piercing plugs was examined. Results were shown in Table 1 as plug life ratios. The plug life ratios were evaluated by using a conventional plug made of 3Cr-1Ni as comparative example.
  • Comparative Examples 1 and 2 and Example 1 of the embodiment 1 using plugs made of pure Mo were subjected to a comparison, thus resulting in that a fact being found that the life of the plug according to the embodiment 1 having the steel plate joined to the leading end surface of the billet can be elongated as compared with the plug according to Comparative Example 2 having no steel plate joined as described above.
  • the plug according to Comparative Example 2 encountered cracks.
  • Example in which the steel plate was joined to each of the two sides of the end surfaces resulted in a simile effect being obtained to that obtained in the case where the steel plate was joined to the leading end surface.
  • Comparative Example 3 and Example 2 of the embodiment 1 each using a plug made of TZM were subjected to a comparison, thus resulting in a fact being known that the life of the plug having the steel plate joined to the leading end surface of the billet can be elongated. Comparative Example 3 encountered cracks.
  • Example 3 using a plug made of TZC and Example 4 using a plug made of JIS-SUH31 resulted in the life of the plug being elongated because the steel plate was joined to the leading end surface of the billet.
  • a plug body 1 was made of SKD61 employed by the conventional plug and a hard layer 2 composed variously as shown in Table 2 was formed on the surface of the plug body 1.
  • a piercing plug having a shape shown in Fig. 2 was used to pierce the billet. The life of each of the used piercing plugs was examined. Results were shown in Table 2 as the plug life ratios. The plug life ratios were evaluated by using the life of the plug according to Comparative Example 1.
  • Example 6 in which WC-Co was, as the main component of the hard layer 2, added to stellite and Example 7 in which Cr2C was added to stellite resulted in the life of the plug being further elongated as compared with Example 5 in which the hard layer 2 was made of only stellite.
  • a piercing plug consisting of a plug body 1 made of S45C and a plug head 3 joined to the leading end of the plug body by a head joining portion 4 and made of TZM and a piercing plug having the hard layer 2 having the composition shown in Table 3 and formed on the surface of the plug body 1 and that of the plug head 3 were used to pierce the billet.
  • Each piercing plug had the shape as shown in Fig. 3.
  • the life of each of the used piercing plugs was examined. Results were shown in Table 3 as the plug life ratios.
  • the plug life ratios were evaluated by using the life of the plug according to Comparative Example 1.
  • Comparative Example 5 As can be understood from Table 3, comparison of Comparative Example 5 and Example 8 using stellite as the main component of the hard layer 2 resulted in that a fact to be known that the life of the plug according to Example 8 in which the steel plate was joined to the leading end surface of the billet can be elongated. The reason for this is that shortening of the plug due to separation of the hard layer can be prevented. Comparative Example 5 in which the steel plate was not joined to the leading end surface of the billet resulted in a similar effect obtainable from a low-alloy steel plug. Although omitted from Table 3, an Example in which the steel plate was joined to each of the two sides of the end surfaces resulted in a similar effect being obtained to that obtained in the case where the steel plate was joined to the leading end surface.
  • Example 9 The life of the plug according to Example 9 in which WC-Co was added to stellite as the main component of the hard layer 2 and Example 10 in which Cr 2 C was added to stellite resulted in the life being further elongated as compared with Example 8 in which the plug was made of only stellite.
  • the durability of the plug can be improved which raises a problem when a seamless pipe is manufactured which is made of an alloy steel containing at least not lower than 5 wt% Cr or not lower than 5 wt% Ni, or an alloy containing, as the main component, any one of Cr, Ni and Mo.
  • the efficiency in the rolling work can be improved and the tool cost can be reduced.
  • a seamless pipe exhibiting additive value can be manufactured with a low cost.
  • an industrial effect can be obtained.
  • the embodiment 2 of the present invention provides a method for manufacturing a seamless pipe, comprising the steps of :
  • the joining of the steel plate can be performed by welding.
  • the embodiment 2 of the present invention provides a method for manufacturing a seamless pipe, comprising the steps of :
  • the joining of the steel plate can be performed by forcible joining.
  • the billet can be made of an alloy steel containing Cr in an amount of at least 5 wt%, or an alloy steel containing Ni in an amount of at least 5 wt%.
  • the billet can be made of an alloy, the main component of which is selected from the group consisting of Cr, Ni and Mo.
  • the steel plate can be made of a carbon steel.
  • the steel plate can be made of an alloy steel containing one element selected from the group consisting of C in an amount of less than 5 wt%, Cr in an amount of less than 5 wt% and Ni in an amount of less than 5 wt%.
  • the steel plate can be made of an alloy steel containig Si in an amount of 1 wt% or more.
  • Mannesmann piercing or plug piercing has drawbacks in regard to the plug, such as difficulty in external supply of a lubricant for preventing seizure and temperature rise.
  • the piercing process is a severe work, there arises a problem of separation even if the lubricant is, in the form of a coating film, supplied prior to performing the piercing work. Therefore, even the oxide scale film, which is employed most widely, cannot be used in several passes of piercing cycles of an actual rolling operation.
  • a problem in this case is that previous supply of the lubricant encounters wanting of the lubricant during or in several times of the operation, thus causing the plug to be damaged.
  • supply of oxide scale from the billet portion capable of preventing seizure at each piercing work is effective.
  • the foregoing effect can be improved by simply increasing the number of the steel plates to be joined.
  • the foregoing method is performed prior to performing the piercing work, the following two methods are considered to be employed: (1) a method in which a steel plate previously subjected to oxidation treatment (hereinafter called a "previous-oxidized steel plate") is joined prior to performing heating, and then piercing is performed after heating and (2) a method in which the previously-oxidized steel plate is joined to the end surface of the billet after discharge from the heating furnace.
  • the foregoing method (1) can be considered to be the best method because oxidation scale can further be produced in the heating furnace.
  • a steel plate prevents contact between the plug and the billet made of the high-alloy steel as described above so that effects of heat insulating and lubricating the plug are obtained.
  • This is one of characteristics of the embodiment 2. Therefore, if a steel plate which can easily seize with the billet, it is apparent that a satisfactory effect cannot be obtained.
  • a steel plate be joined which contains a component for, in a large quantity, producing FeO or a compound of silicon oxide and iron at high temperature, for example, a general carbon steel, a high silicon steel containing not less than 1 wt% of Si, or a low-alloy steel containing less than 5 wt% C, Cr or Ni.
  • the method of elongating the life of the piercing plug according to the embodiment 2 enables the durability of the piercing plug to be elongated when a billet made of a high-alloy steel or the like is used to manufacture a seamless pipe.
  • the life can be elongated by joining one or more previously-oxidized steel plates to the end surface of the billet and by performing the piercing operation.
  • a high-alloy steel seamless steel pipe or a high-alloy metal seamless pipe can be manufactured by the same pipe manufacturing method while significantly elongating the life of the piercing plug.
  • one or more previously-oxidized steel plates 9 obtained by subjecting a general carbon steel to an oxidation process were, by welding, joined to an end surface (joint position T), on which piercing was commenced, and/or opposite end surface (joint position B) of a billet 8 made of 13Cr steel.
  • a billet to which a steel plate (hereinafter called a "non-oxidized steel plate") which was not subjected to the oxidation process and made of a general carbon steel, and a billet to which no steel plate was joined and made of a general 13Cr steel were used.
  • a piercing plug 1 having a shape shown in Fig. 11 was used.
  • Mannesmann piercing method was employed with an apparatus having a pair of rolls consisting of at least two rolls and two shoes to perform piercing under the following piercing conditions.
  • the previously-oxidized steel plate and the non-oxidized steel plate were joined before the billet 8 was injected into the heating furnace.
  • the piercing plug 1 was made of an alloy steel (hereinafter called a "long-life alloy steel") prepared by adding Mo, V and W, which were components for improving the hot strength, to the conventional steel component (3Cr-1Ni steel) and exhibiting a life ratio of about two times that of the conventional plug when used in piercing.
  • the life of each of the used piercing plugs was examined. Results were shown in Fig. 12 and Table 5 as plug life ratios.
  • the plug life ratios were evaluated by using Comparative Example 1, in which no steel plate was joined to the steel plate, as the reference.
  • Example 1 in which the previously-oxidized steel plate was joined to the leading end surface of the billet, enabled the life of the plug to be elongated as compared with Comparative Example (general piercing) in which the billet alone was used.
  • Comparative Example 2 and Example 1 were subjected to a comparison, thus resulting in that Example 1 to which the previously-oxidized steel plate was joined to the end surface of the billet enabled the life of the plug to be elongated as compared with Comparative Example 2.
  • Example 2 was performed under the same piercing conditions as those employed in Example 1 except joining of the previously-oxidized steel plate (the non-oxidized steel plate was employed in the comparative example) to the billet being performed after discharge from the heating furnace.
  • the previously-oxidized steel plate (the non-oxidized steel plate was employed in the comparative example) was joined by press fitting when centering was performed after discharge from the heating furnace.
  • the life of the plug after piercing was performed was examined. Results were shown in Fig. 13 and Table 6 as the plug life ratio.
  • Example 2 As can be understood from Fig. 13 and Table 6, an effect of elongating the life of the plug was obtained from Example 2 although it was somewhat shorter than that obtained in Example 1. Also in Example 2, a satisfactory effect was obtained due to increase in the previously-oxidized steel plates as can be understood from Examples 9 and 10.
  • Example 3 was performed under the same piercing conditions as those employed in Example 1 except the components of the previously-oxidized steel plate being varied. The life of the plug after piercing was performed was examined. Results were shown in Table 7 as the plug life ratio. Steel Plate Timing Plug Life Ratio Joint Posiiton Evaluation Remarks Type No.
  • Comparative Examples 5 to 9 in which a 5Cr steel plate, a 9Cr steel plate, a 13Cr steel plate, SUS304 and SUS316 steel plates containing components similar to those of the 13Cr steel plate selected as the base for the billet resulted in unsatisfactory effect of elongating the life of the plug.
  • Comparative Examples 7 and 9 resulted in deterioration.
  • Examples 11, 12 and 13 in which the low-alloy steel, such as the general carbon steel plate, a 1Cr steel plate, a 2.25Cr steel plate, was employed resulted in apparent effect of elongating the life of the plug.
  • a similar effect was obtained in the case where high Ni alloy steel (content of Ni: not less than 5 wt%) or an alloy, the main component of which was Cr, Ni or Mo was employed as the base for the billet.
  • a problem of unsatisfactory durability of the plug which arises when a seamless pipe made of an alloy steel containing not less than 5 wt% of Cr or not less than 5 wt% of Ni or an alloy, the main component of which is Cr, Ni or Mo, is manufactured can be improved.
  • the efficiency in the rolling work can be improved and the tool cost can be reduced.
  • a seamless pipe having additive values can be manufactured with a low cost.
  • an industrial effect can be obtained.
  • Fig. 14 shows the shape of the plug.
  • reference numeral 1 represents the plug
  • 12 represents a piercing roll.
  • Lp represents the effective length of the plug
  • L1 represents the length of the plug rolling portion
  • L2 represents the length of the plug reeling portion
  • L3 represents the relief length of the plug.
  • the overall length L of the plug is Lp + L3.
  • Dp represents the diameter of the plug
  • R1 represents the radius of the plug reeling portion
  • r represents the radius of the leading end of the plug
  • ⁇ represents the angle of the plug reeling portion
  • ⁇ represents the angle of the roll outlet portion.
  • a plug As disclosed in, for example, Elongated Steels, Steel Pipes and Common Facilities for Rolling, Steel Handbook III (2) edited by Japan Steel Association, Elongated Steel, pp. 935 and 936, design of a plug has been performed such that the plug consists of a leading end, a body and a relief portion.
  • the front portion of the body has a rolling portion for mainly reducing the thickness and a reeling portion for finishing and obtaining the desired thickness.
  • the reeling angle ⁇ is basically considered to be in parallel to the angle ⁇ of the outlet portion of the rolls. Therefore, ⁇ - ⁇ is 0° in the foregoing case. In general, ⁇ - ⁇ is made to be less than ⁇ 0.8°.
  • the length of the reeling portion is, in many cases, made to be 1.0 time to 1.5 times with which the pre-processed pipe can be moved forwards.
  • a plug capable of performing a piercing work while preventing thickness deviation has been disclosed having a structure such that the diameter of the plug is 141 mm, length of the same is 309 mm, the length of the reeling portion is 120 mm and the angle of the reeling portion is 2.5° when the angle ⁇ at the outlet portion of rolls is 3° and the inclination of the roll is 13°.
  • ⁇ - ⁇ is - 0.5. Examples of the foregoing case are shown in comparison with Comparative Examples A and B in Table 8.
  • the embodiment 3 is a characterized by a piercing plug for manufacturing a seamless pipe for use to pierce a billet made of a high alloy or a high-alloy steel for manufacturing a seamless pipe, the piercing plug for manufacturing a seamless pipe being characterized in that size of the plug satisfies the following equation: 0.8° ⁇ ⁇ - ⁇ ⁇ 1.5° where ⁇ is an angle of plug reeling portion, and ⁇ is an angle at the outlet portion of a roll.
  • the embodiment 3 is characterized by a method of manufacturing a seamless pipe for manufacturing a seamless pipe by using a billet made of a high alloy or a high-alloy steel, the method comprising the step of using the plug for manufacturing a seamless pipe.
  • the embodiment 3 is characterized by a method of manufacturing a seamless pipe for a seamless pipe by using a billet made of a high alloy or a high-alloy steel, the method comprising the steps of joining a steel plate to a leading end of the billet in the moving direction, and piercing the billet by using the plug for manufacturing a seamless pipe.
  • the piercing plug for manufacturing a seamless pipe has the structure such that the angle ⁇ of the plug reeling portion is set to be the foregoing large range with respect to the angle ⁇ of the roll outlet portion. Therefore, the pressure of the plug contact surface can be reduced and, thus, the damage of the surface of the plug can be prevented. As a result, the life of the plug can effectively be elongated.
  • the reason why ⁇ - ⁇ is limited to be 0.8° or larger is as follows. If the angle is smaller than 0.8°, the pressure of the contact surface cannot be reduced as desired and, therefore, the effect of elongating the life of the plug is unsatisfactory.
  • the angle ⁇ - ⁇ is set to be 1.5° or smaller.
  • the plug cost can be reduced satisfactorily.
  • the time required to change the plug can be shortened and deterioration in the efficiency in the rolling work can be prevented.
  • the method of manufacturing a seamless pipe has the structure such that a steel plate is joined to the leading end in the direction in which the billet is moved forwards in addition to the foregoing structure. Therefore, joining of the steel plate causes the life of the plug to be elongated as follows.
  • the oxidation scale is not generated in a large quantity when a high alloy or high-alloy steel billet is pierced, the oxidation scale cannot be supplied to the surface of the plug. Thus, the life of the plug is shortened excessively. To considerably elongate the life of the plug when used to pierce a high alloy or a high-alloy steel, oxidation scale must be supplied to the surface of the plug in a quantity larger than the quantity which is consumed.
  • the method of manufacturing a seamless pipe has the structure such that the steel plate is joined to the leading end of the billet in the direction in which the same is moved forwards, followed by being injected into the heating furnace so that oxidation scale is produced on the end surface of the billet.
  • the oxidation scale produced on the end surface of the billet can be supplied to the leading end of the plug. Therefore, life of the plug can significantly be elongated.
  • Piercing conditions were set to be as shown in Table 8.
  • Examples 1 to 4 had the size and piercing conditions of the plug according to the embodiment 3, while Comparative Example 5 had the size and piercing conditions of the conventional plug.
  • the plug life ratios were as indicated by No. 1 and 2 shown in Table 9.
  • the conventional plug having usual size was employed as the reference to which no steel plate was joined to the leading end of the plug to pierce the billet as indicated by No. 5 shown in Table 9.
  • Fig. 16 shows an example of the pressure of the plug contact surface.
  • the peak of the pressure of the contact surface was reduced by 10 % to 15 %. Thus, it can be considered that the life of the plug can be elongated.
  • a billet 8 to which a steel plate 9 was joined to the leading end thereof in the moving direction such that the steel plate was joined to the leading end surface of the billet, and a conventional billet having no steel plate joined thereto were subjected to a comparison about the life of the plug in such a manner that the plug according to the embodiment 3 and a conventional plug made of a 13Cr steel was subjected to the comparison.
  • the piercing conditions were the same as those employed in Example 1.
  • the plug life ratios were as indicated by No. 3 and 4 shown in Table 9. As can be understood from Table 9, use of the plug according to the embodiment 3 and joining of the steel plate to the billet to perform piercing resulted in the life being elongated to about four times.

Claims (16)

  1. Verfahren zur Herstellung eines nahtlosen Rohres, welches die Schritte aufweist:
    a. Präparieren eines Walzblocks, welcher aus einem Legierungsstahl oder einer Legierung hergestellt ist;
    b. Verbinden einer Stahlplatte zu zumindest einer Endfläche des Walzblocks, an welcher ein Piercen des Walzblocks zu beginnen ist;
    c. Heißpiercen des Walzblocks bei einer Hochtemperatur mit einem Piercingstopfen durch ein Mannesmann-Piercing, um eine hohle Hülle zu produzieren, wobei ein Oxidblech von der Stahlplatte bei der Hochpiercingtemperatur ausgebildet wird, wobei das Oxidblech den Piercingstopfen während des Heißpiercens mit einer Schmierung versorgt;
    d. Walzen der hohlen Hülle, um ein nahtloses Rohr herzustellen; und
    e. entweder Heizen des Walzblocks, nach Schritt (a) mit der Heizofentemperatur oder Heizen des Walzblocks, an welchem die Stahlplatte nach Schritt (b) verbunden ist;
    wobei der Piercingstopfen und eine Walze die folgende Gleichung erfüllen: 0,8° < α - β < 1,5°, wobei α ein Winkel eines Stopfenwickelabschnitts ist and β ein Winkel an einem Auslassabschnitt der Walze ist.
  2. Verfahren nach Anspruch 1, wobei der Walzblock eine Stahllegierung aufweist, welche Cr in einem Betrag von zumindest 5 Gew.-% enthält.
  3. Verfahren nach Anspruch 1, wobei der Walzblock einen Legierungsstahl aufweist, welcher Nickel in einem Betrag von zumindest 5 Gew.-% enthält.
  4. Verfahren nach Anspruch 1, wobei der Wälzblock eine Legierung aufweist, dessen Hauptkomponente aus der Gruppe ausgewählt ist, welche Cr, Ni und Mo enthält.
  5. Verfahren nach zumindest einem der Ansprüche 1 bis 4, wobei der Piercingstopfen aus Mo, einer Mo-Legierung oder einem warmfesten Stahl hergestellt ist.
  6. Verfahren nach Anspruch 1, wobei der Piercingstopfen aufweist:
    einen Hauptkörper, welcher aus Mo, einer Mo-Legierung oder einem warmfesten Stahl hergestellt ist; und
    eine harte Schicht, welche an der Oberfläche des Hauptkörpers ausgebildet ist.
  7. Verfahren nach zumindest einem der Ansprüche 1 bis 5, wobei der Piercingstopfen aufweist:
    einen Stopfenkörper, welcher aus Mo, einer Mo-Legierung oder einem warmfesten Stahl hergestellt ist; und
    einen Stopfenkopf, welcher an einem Führungsende des Stopfenkörpers ausgebildet ist und aus Mo, einer Mo-Legierung oder einem warmfesten Stahl hergestellt ist.
  8. Verfahren nach Anspruch 7, wobei der Stopfenkörper eine gehärtete Schicht aufweist, welche an einer Oberfläche des Stopfenkörpers ausgebildet ist.
  9. Verfahren nach Anspruch 7 oder 8, wobei der Stopfenkopf eine harte Schicht aufweist, die an einer Oberfläche des Stopfenkopfs ausgebildet ist.
  10. Verfahren nach Anspruch 6, 8 oder 9, wobei die harte Schicht aus einem Material hergestellt ist, welches aus der Gruppe ausgewählt ist, die aus Stellit, Keramiken, welche durch Hinzufügung von Wolframcarbid zu Stellit erhalten werden, Keramiken, welche durch Hinzufügung einer Mischung von Wolframcarbid und Kobalt zu Stellit erhalten werden, sowie Keramiken, welche durch Hinzufügung eines Verbunds von Chrom und Kohlenstoff zu Stellit erhalten werden.
  11. Verfahren nach Anspruch 1, wobei die Stahlplatte einen Kohlenstoffstahl aufweist.
  12. Verfahren nach Anspruch 1, wobei die Stahlplatte einen Legierungsstahl aufweist, welche ein Element enthält, das aus der Gruppe ausgebildet ist, welche aus Kohlenstoff in einem Betrag von weniger als 5 Gew.-%, Cr in einem Betrag von weniger als 5 Gew.-% und Ni in einem Betrag von weniger als 5 Gew.-% besteht.
  13. Verfahren nach Anspruch 1, wobei die Stahlplatte einen Legierungsstahl aufweist, welcher Si in einem Betrag von 1 Gew.-% oder mehr enthält.
  14. Verfahren nach Anspruch 1, wobei die Verbindung der Stahlplatte durch Schweißen durchgeführt wird.
  15. Verfahren nach Anspruch 1, wobei die Verbindung der Stahlplatte durch ein Verbinden unter Zwang durchgeführt wird.
  16. Verfahren nach Anspruch 1, wobei die Stahlplatte einer Oxidationsbehandlung unterzogen wird.
EP96107907A 1995-05-19 1996-05-17 Verfahren zur Herstellung eines nahtlosen Rohres Expired - Lifetime EP0743106B1 (de)

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JP14567395 1995-05-19
JP145673/95 1995-05-19
JP14567395A JPH08309408A (ja) 1995-05-19 1995-05-19 穿孔プラグ耐用度に優れた継目無管の製造方法
JP16282495 1995-06-06
JP162824/95 1995-06-06
JP16282495A JPH08332504A (ja) 1995-06-06 1995-06-06 穿孔プラグ耐用度に優れた継目無管の製造方法
JP16863495 1995-07-04
JP168634/95 1995-07-04
JP07168634A JP3085149B2 (ja) 1995-07-04 1995-07-04 継目無管製造用穿孔プラグ及び継目無管製造方法

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US5778714A (en) 1998-07-14
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US6073331A (en) 2000-06-13
EP0743106A1 (de) 1996-11-20
DE69617797D1 (de) 2002-01-24

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